com.opensymphony.xwork2.validator

## Interface ValidatorFactory

- All Known Implementing Classes:
    DefaultValidatorFactory

      public interface ValidatorFactory

  ValidatorFactory

  Validation rules are handled by validators, which must be registered with the ValidatorFactory (using the registerValidator method). The simplest way to do so is to add a file name validators.xml in the root of the classpath (/WEB-INF/classes) that declares all the validators you intend to use.

  INFORMATION validators.xml if being defined should be available in the classpath. However this is not necessary, if no custom validator is needed. Predefined sets of validators will automatically be picked up when defined in com/opensymphony/xwork2/validator/validators/default.xml packaged in in the xwork jar file. See ValidatorFactory static block for details.

  WARNING If custom validator is being defined and a validators.xml is created and place in the classpath, do remember to copy all the other pre-defined validators that is needed into the validators.xml as if not they will not be registered. Once a validators.xml is detected in the classpath, the default one (com/opensymphony/xwork2/validator/validators/default.xml) will not be loaded. It is only loaded when a custom validators.xml cannot be found in the classpath. Be careful.

  Note: The default validationWorkflowStack already includes this.
  All that is required to enable validation for an Action is to put the ValidationInterceptor in the interceptor refs of the action (see xwork.xml) like so:

           <interceptor name="validator" class="com.opensymphony.xwork2.validator.ValidationInterceptor"/>

  Field Validators Field validators, as the name indicate, act on single fields accessible through an action. A validator, in contrast, is more generic and can do validations in the full action context, involving more than one field (or even no field at all) in validation rule. Most validations can be defined on per field basis. This should be preferred over non-field validation wherever possible, as field validator messages are bound to the related field and will be presented next to the corresponding input element in the respecting view.

  Non Field Validators Non-field validators only add action level messages. Non-field validators are mostly domain specific and therefore offer custom implementations. The most important standard non-field validator provided by XWork is ExpressionValidator.

  NOTE: Non-field validators takes precedence over field validators regardless of the order they are defined in *-validation.xml. If a non-field validator is short-circuited, it will causes its non-field validator to not being executed. See validation framework documentation for more info.

  VALIDATION RULES:

  Validation rules can be specified:

  1. Per Action class: in a file named ActionName-validation.xml
  2. Per Action alias: in a file named ActionName-alias-validation.xml
  3. Inheritance hierarchy and interfaces implemented by Action class: XWork searches up the inheritance tree of the action to find default validations for parent classes of the Action and interfaces implemented

  Here is an example for SimpleAction-validation.xml:

       <!DOCTYPE validators PUBLIC "-//Apache Struts//XWork Validator 1.0.3//EN"
                      "http://struts.apache.org/dtds/xwork-validator-1.0.3.dtd">
       <validators>
         <field name="bar">
             <field-validator type="required">
                 <message>You must enter a value for bar.</message>
             </field-validator>
             <field-validator type="int">
                 <param name="min">6</param>
                 <param name="max">10</param>
                 <message>bar must be between ${min} and ${max}, current value is ${bar}.</message>
             </field-validator>
         </field>
         <field name="bar2">
             <field-validator type="regex">
                 <param name="expression">[0-9],[0-9]</param>
                 <message>The value of bar2 must be in the format "x, y", where x and y are between 0 and 9</message>
            </field-validator>
         </field>
         <field name="date">
             <field-validator type="date">
                 <param name="min">12/22/2002</param>
                 <param name="max">12/25/2002</param>
                 <message>The date must be between 12-22-2002 and 12-25-2002.</message>
             </field-validator>
         </field>
         <field name="foo">
             <field-validator type="int">
                 <param name="min">0</param>
                 <param name="max">100</param>
                 <message key="foo.range">Could not find foo.range!</message>
             </field-validator>
         </field>
         <validator type="expression">
             <param name="expression">foo lt bar </param>
             <message>Foo must be greater than Bar. Foo = ${foo}, Bar = ${bar}.</message>
         </validator>
       </validators>

  Here we can see the configuration of validators for the SimpleAction class. Validators (and field-validators) must have a type attribute, which refers to a name of an Validator registered with the ValidatorFactory as above. Validator elements may also have <param> elements with name and value attributes to set arbitrary parameters into the Validator instance. See below for discussion of the message element.

  Each Validator or Field-Validator element must define one message element inside the validator element body. The message element has 1 attributes, key which is not required. The body of the message tag is taken as the default message which should be added to the Action if the validator fails. Key gives a message key to look up in the Action's ResourceBundles using getText() from LocaleAware if the Action implements that interface (as ActionSupport does). This provides for Localized messages based on the Locale of the user making the request (or whatever Locale you've set into the LocaleAware Action). After either retrieving the message from the ResourceBundle using the Key value, or using the Default message, the current Validator is pushed onto the ValueStack, then the message is parsed for \$\{...\} sections which are replaced with the evaluated value of the string between the \$\{ and \}. This allows you to parameterize your messages with values from the Validator, the Action, or both.

  If the validator fails, the validator is pushed onto the ValueStack and the message - either the default or the locale-specific one if the key attribute is defined (and such a message exists) - is parsed for ${...} sections which are replaced with the evaluated value of the string between the ${ and }. This allows you to parameterize your messages with values from the validator, the Action, or both.

  NOTE: Since validation rules are in an XML file, you must make sure you escape special characters. For example, notice that in the expression validator rule above we use "&gt;" instead of ">". Consult a resource on XML for the full list of characters that must be escaped. The most commonly used characters that must be escaped are: & (use &amp;), > (user &gt;), and < (use &lt;).

  Here is an example of a parameterized message:

  This will pull the min and max parameters from the IntRangeFieldValidator and the value of bar from the Action.

          bar must be between ${min} and ${max}, current value is ${bar}.

  Another notable fact is that the provided message value is capable of containing OGNL expressions. Keeping this in mind, it is possible to construct quite sophisticated messages.

  See the following example to get an impression:

          <message>${getText("validation.failednotice")}! ${getText("reason")}: ${getText("validation.inputrequired")}</message>

  Author:
    Jason Carreira, James House

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `Validator` | `getValidator(ValidatorConfig cfg)` Get a Validator that matches the given configuration.
    `String` | `lookupRegisteredValidatorType(String name)` Lookup to get the FQ classname of the given validator name.
    `void` | `registerValidator(String name, String className)` Registers the given validator to the existing map of validators.

- - ### Method Detail

    - #### getValidator

          Validator getValidator(ValidatorConfig cfg)

      Get a Validator that matches the given configuration.
      Parameters:
        `cfg` - the configurator.
      Returns:
        the validator.

    - #### registerValidator

          void registerValidator(String name,
                               String className)

      Registers the given validator to the existing map of validators. This will add to the existing list.
      Parameters:
        `name` - name of validator to add.
        `className` - the FQ classname of the validator.

    - #### lookupRegisteredValidatorType

          String lookupRegisteredValidatorType(String name)

      Lookup to get the FQ classname of the given validator name.
      Parameters:
        `name` - name of validator to lookup.
      Returns:
        the found FQ classname
      Throws:
        `IllegalArgumentException` - is thrown if the name is not found.

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